The present invention generally relates to a power amplifier system used in telecommunication systems and more specifically to an adaptive system for efficiently combining and transmitting signals created by one or more power amplifiers.
Wireless communication signals received by antennas are often very weak. Therefore, power amplifiers are widely used in wireless transmission systems to increase the signal strength of the received wireless signal. Oftentimes, wireless transmission systems will utilize more than one power amplifier. For example, a plurality of amplifiers may be required because several different carrier signals must be amplified separately. In another scenario, more than one amplifier is required to provide an output signal with the requisite signal strength. The outputs of the plurality of amplifiers is commonly combined into a single output signal by a signal combiner.
Generally, two classes of power amplifiers exist for handling different types of transmission signals. Multi-Carrier Power Amplifiers (MCPAs) are used in amplifier modules designed to handle wideband signals (i.e., signals containing more than one carrier frequency). MCPAs are used to amplify signals containing multiple carriers. An alternative to MCPAs, are Single Carrier Power Amplifiers (SCPAs). SCPAs are limited to amplifying signals containing essentially only one carrier frequency. Therefore, before using an SCPA, a wideband signal having multiple carriers must be divided into individual signals, each generally containing only one carrier frequency. Each of these single carrier signals is then amplified by a separate SCPA.
The use of MCPAs offers a cost effective alternative to the use of numerous SCPAs for applications requiring high signal density in a wireless base station. However, utilizing a single MCPA has certain drawbacks. If a single MCPA fails in the operating environment, it has the potential of disabling the entire wideband transmission signal, including all the associated carrier frequencies, as opposed to affecting only one carrier frequency if an SCPA were to fail. Therefore, a level of redundancy is desirable for MCPAs implemented within a power amplifier scheme of a transmission system. Such a system of redundancy would also be useful in SCPA systems. Such redundancy would ensure that all of the carrier signals are not lost due to a single amplifier failure.
It is also often desirable to increase the number of carriers that may be amplified by an SCPA system. Such a system must allow additional SCPAs to be easily added to the power amplifier system.
Within a wireless transmission system, it is often desirable to upgrade or modify the system by adding additional amplification. Since the output power is increased by either replacing existing power amplifiers or adding additional amplifiers, such a system must allow for easy replacement of existing MCPAs or SCPAs or allow for the addition of more MCPAs or SCPAs.
When providing or modifying the amplification features of a wireless system to address such objectives, one possible solution is to construct a combining network consisting of multiple power amplifiers, which also allows additional amplifiers to be added. It also should provide for the amplifiers to be easily removed and replaced if necessary. However, several obstacles must be overcome in order for such a network to be cost effective and efficient.
First, the impedance of the output line of a combiner will vary depending upon the amplifiers in the system. Therefore, the system must address the issue of varying line characteristics at the output of a signal combiner, such as the impedance of the output line, based upon the number of MCPAs or SCPAs inserted within the system. This is an important consideration in order to ensure an efficient transfer of the amplified signals from the signal combiner to the output lines.
Additionally, a system with multiple ports for accepting power amplifiers will experience various levels of input signal loss if any of the ports are empty. Therefore, a solution to the above objectives must address input signal losses based upon the number of ports containing power amplifiers within the system.
Still further considerations involve the types of components utilized in the signal combining network. Conventional systems with multiple power amplifiers often use a large number of switches in order to control the flow of input signals to the various amplifiers. Such switches have various drawbacks. First, switches are inherently lossy electrical devices. Therefore, signal strength decreases each time a signal passes through a switch. Secondly, since switches are mechanical devices, they have a certain degree of unreliability because they are prone to failure. Therefore, a solution to various of the above-discussed issues should also address such unreliability, switch failures, minimize signal loss from switching components, and improve the robustness of the overall system.